In a quantum computer having a quantum dot, it is necessary that a spin state of an electron inside the quantum dot is read out. To this date, a read-out method using a single electron transistor (Nonpatent document 1 and Nonpatent document 2), a read-out method emitting a light to the quantum dot to read out from a polarized light emission intensity (Nonpatent document 3), and so forth are proposed.
However, in the method using the single electron transistor, there is a problem of requiring a complicated structure in addition to a problem of a shorter coherence lifetime. Moreover, the size of the single electron transistor itself increases as well.
Further, in the method of exciting the quantum dot by light, an interaction is caused between an exciton and an electron in the quantum dot in that the light is emitted directly to the quantum dot. Therefore, there is a possibility that correct information could not be read out due to a variation of a spin state of the electron.
Patent document 1: Japanese Patent Application Laid-Open No. 2004-103952
Patent document 2: Japanese Patent Application Laid-Open No. 2000-68495
Patent document 3: Japanese Patent Application Laid-Open No. 2003-86788
Patent document 4: Japanese Patent Application Laid-Open No. 2003-338618
Nonpatent document 1: J. M. Elzerman et al., Nature 430, 431 (2004)
Nonpatent document 2: M. Friesen et al., Phys. Rev. Lett. 92, 037901 (2004)
Nonpatent document 3: A. Shabaev et al., Phys. Rev. B 68, 201305R (2003)
Nonpatent document 4: J. M. Garcia et al. Appl. Phys. Lett. 71, 2014 (1997)